The Diels-Alder adduct of myrcenol and acrolein is known in the art to consist of a mixture of I and II as illustrated below: ##STR1## When the reaction is uncatalysed (thermal) the ratio of I:II is about 3:1. In a catalysed reaction, I predominates even more and the ratio is more like 9:1. The art concerning the catalysed and uncatalysed reaction is provided in detail in U.S. Pat. No. 4,007,137.
The art also teaches processes to convert myrcene to myrcenol. In order to accomplish this, the diene portion of the myrcene must be protected before hydrating the isolated double bond. For example, U.S. Pat. No. 3,176,022 discloses a method wherein a cyclic sulfone is prepared by reacting myrcene with sulfur dioxide, the diene portion reacting with the sulfur dioxide in a Diels Alder type reaction. This myrcene sulfone was then hydrated and the resulting tertiary alcohol was heated to regenerate the diene and provide the desired myrcenol.
U.S. Pat. No. 3,932,539 teaches the preparation of a mixture of terpene alcohols consisting essentially of myrcenol and at least 20% cis-ocimenol and trans-ocimenol. According to this teaching, myrcene is hydrochlorinated to a mixture of linalyl chloride (ca. 10%), neryl and geranyl chlorides. These chlorides are reacted with a tertiary amine (trimethyl amine) to provide a quaternary ammonium salt which was then hydrated to form mixtures of cis and trans 3,7-dimethyl-7-hydroxy-2-octen-1-yl trimethyl ammonium chlorides. The chlorides are then converted to the hydroxides and thermally decomposed (Hofmann elimination) to provide a mixture of myrcenol, cis-ocimenol and trans-ocimenol.
Whereas a pure myrcenol was prepared via the sulfone intermediate (U.S. Pat. No. 3,176,022), the process utilizing the quaternary ammonium salt (U.S. Pat. No. 3,932,539) provided a mixture of myrcenol and ocimenols. Such a mixture of myrcenol, cis-ocimenol and trans-ocimenol is unsuitable for the preparation of Diels-Alder adducts such as 3 and 4-(4-methyl-4-hydroxyamyl)-.DELTA..sup.3 -cyclohexanecarboxaldehyde since it is reported (U.S. Pat. No. 3,758,590) that ocimenol will react with acrolein to produce an adduct of its own.
It should be noted that while U.S. Pat. No. 3,758,590 does not appear to distinguish whether an adduct is formed from both cis-ocimenol and trans-ocimenol or only from one of these isomers, it is only the trans-ocimenol that is capable of forming an adduct with acrolein.